Closed feed system for steam power plants



Oct. 6, 1953 H. HILLIER 2,654,581

CLOSED FEED SYSTEM FOR STEAM POWER PLANTS Filed March 20, 1951 v 2 Sheets-Sheet 1 Oct. 6, 1953 H. HILLIER 2,654,581

CLOSED FEED SYSTEM FOR STEAM POWER PLANTS Filed March 20, 1951 2 Sheets-Sheet 2 Patented Oct. 6, 1953 CLOSEDFEED 'SY S TEM FOR'" STEAM POWER PLANTS Harold Hillier Glasgow, Scotland; assignor. to. G; & J1 Weir Limited, Glasgow, scotlandgflva' corporation of Great Britain" and Northern Ireland Application Marclr20, 1951;, ScrialNmZlfiAttl: InGreat Britain May-11,1950.

9 Claims; I

This invention" relates to closedlfeedsystems.

fer steamipower "plants of the class including a v steam generator, a turbinaa steam condenser. andtheassociatedifeecl, water and steam connece tions, andmore' particularly, to. such feed systems'incorpor'ating'a deaerator separate from the condenser:

Arr object ofthe invention is to provide an arrangement whereby" such closed feed system can-*beoperatedentirely automatically in a stable and satisfactory manner andi'wherebytwo or. more closedfeedsystems can betoperatedentirely satisfactorily and. stably in parallellwith a minimumflow' ofifeed'iwater into and. out. of the system or systems.

A cl'osed feed systemis accordancewith ourinvention includes in its simplest form a condenser; a condenser extraction pump, 7 an external. feed tank"; a deaeratorinto which condensate isdischarged by the condenser extraction. pump, a deaerator extraction pump and a. boiler feed pump, and is characterised by control devices which maintain a substantially constant flow of water through the condenser extraction. pump.

and the deaerator extractionv pump at substantially' predetermined constant discharge; pres.- suresat'the discharges of saidpumps, the discharge pressure of theideaerator extractionpump beingsubstantially greater than'the pressure due to the head of water in the feed tank or/and'. the

pressure on the-surface of that water. available to cause the outflow of water from the feedtank to the boiler feed pump,

Preferably, the steam condenser. isOf the TB? generative type devised to remove. corrosive gasesfrom'the-feed water passingthrough the con.- denser and thereby to ensure that the.feed..water removed from the condenser and discharged towards the boiler feed pumpwill. be as. free as possible fromlcorrosive'gases.

Withthe'a'doption of higher pressures in boiler.

installations now in use. in powerplants, it is essential thatevery possible trace. ofroxygen or. other corrosive gases. should be: removed from the water before. it is discharged into the boileers; and every, possible precautionrshould, there fore, be taken to. remove every trace of corrosive gases from the water and prevent any possible ingress ofcorrosive gases or of. Water contaminated'with corrosive gases. For this-purpose, a float-controlled valve mounted on the steam condenser is so arranged'that it can pass into the condenser a quantity of'water equal to the maximum capacity of the condenser extracticnpump and the condenser extraction pump is so. designed the regenerative. steam condenser. operation; there is no'flow'of water from the feed;

that 'its'maximum capacity is" equaltoorrslightly in excess, of the maximumcapacityof 'the'boiler feed pump or'pumps with which it. isl'a'ssociated.

The condenser extraction .pump'is-so' devised that it is capable of handling its maximum capacity with a water levelon its suction'side lower than;

feed-lpumpj so that there is" an appreciable pressurei'aboveiatmosphere: int the: pipe between the condenser" extraction; pump and the boiler feed pump'which prevents the ingressof air'land corrosive i gases intothe waterin. the pipe line between' the condenser" extraction pump and-the boiler feed pumpr pipe'connects the feed tank to the pipe between the condenser: extraction pumpand' the boiler feed pump to allow theboiler feed" pump to draw water direct from the. feed tank in" the eventpffailure' ofthecondenser extraction pump. The boiler 'feed pump operates atits maximum capacityon'ly' in case of emergency and'itsactual;deliveryvaries in quantity so that there is a continuous flow" of water from the condenserextractionfpump discharge up the pipe connected to: the feed. tank. The water which'ispassingup towards the: feed 'tank', however, p-assesback-by'way of the fioatecontrolled valve into'thesteam condenser, so that a, varyingquantityof water is being continuously circulatedthrough the'floatmontrolled valve and repeatedly'subiected to" the deaerating action of tankdirect into the-feedisystem; butin the. event ofa stoppageof the condenser'extraction pump theboilerfeedpump will drawwater direct: from the feed tank": Innormal operation the dischargepressure" of the condenser extraction pump-"is determined by the head imposedb'y' the feed tanlr'and tliat-there is'notpossibility of water which maybe-contaminatedpassing direct into' the'ieed system;

Two or*moresteam condensing plants together crate, in parallel; the quantities J of condensate: formed in the condensers; ,being; discharged into In normal 3 the feed system at a common marrying point and ressure.

In some power installations, as, for example, on board ship, it may not be practical or convenient for the feed tank to be arranged at an elevated position and in such cases pressure loading means may be provided to ensure a reasonable pressure above the atmosphere in the piping between the condenser extraction pump, the boiler feed pump and the feed tank.

As even when operated in the manner described regenerative steam condensers do not remove all possible traces of corrosive gases from the condensate and feed water, there is arranged in the feed system a deaerator wherein all the water which in normal operation passes to the boiler feed pump is subjected to a further deaerating action so as to ensure that all the corrosive gases in the feed water are removed before the water is delivered to the boiler. Water inlet to the said deaerator is connected to the discharge of the condenser extraction pump at a point between the discharge of that pump and the connection to the float-controlled valve of the steam condenser. There may be arranged in the water inlet pipe line to the deaerator a float-controlled valve with the float actuated from a Water level in the base of the deaerator so that on a rise in water level in the deaerator the flow of such water into the deaerator is reduced and vice versa. The deaerator is provided with a deaerator extraction pump which delivers the deaerated feed water into the suction of the boiler feed pump. The pipe connection between the deaerator extraction pump and the boiler feed pump is also connected by a pipe to the feed tank, and in this pipe line there is provided a non-return valve which prevents any possibility of deaerated water from the deaerator being discharged back to the feed tank, whereas on failure of the deaerator or deaerator extraction pump, water can flow direct from the feed tank through the said non-return valve into the suction of the boiler feed pump, thereby ensuring the continuity of the feed supply to the boiler.

The. discharge of the deaerator extraction pumpi connected to the top of the deaerator whereby the deaerator extraction pump is constrained to operate at substantially constant car pacity at all times and at a predetermined subr stantially constant discharge pressure in excess of a the head of the feed tank, so that the non-return valve in the connection between the feed tank and the boiler feed pump suction is held closedin normal operation and the deaerator extraction pump discharge pressure is'held substantially constant at such pressure above the deaerator pressure as will ensure the satisfactory operation of the boiler feed pump.

In modern feed systems the additive effect of pumps in series in the feed system with stable discharge pressure capacity characteristics is to give a very high total discharge pressure at no loadas compared with full load pressure, thereby involving a corresponding increase in design scantlings and cost.

'With the arrangement according to the invention, the rise in discharge pressure of the boiler feed pump between full load and no load is limited to the characteristic of the boiler feed pump only, and the, total load of the boilers may be shared between two or more boiler feed pumps in operation in proportion to their respective designed maximum capacities. deaerator extraction pump is arranged 0 be For this purpose, the s The capacity of the equal to or greater than the boiler feed pump capacity, and since the boiler feed pump never discharges at maximum capacity in normal operation, there is always a flow of water from the deaerator extraction pump into the deaerator, so that water flowing in this manner is subjected to repeated deaerating action. The return of such water to the deaerator may be controlled by a float-controlled valve with the float actuated from the water level in the deaerator so that the valve is closed as the water level rises and vice versa, or there may be provided a spring-loaded valve or a pressure-biased and controlled valve to maintain a substantially constant pressure difference across the deaerator extraction pump. Control mechanism may be provided to control the flow of heating steam to the deaerator to maintain a substantially constant pressure in the deaerator.

In the accompanying drawings Fig. 1 shows diagrammatically a boiler feed system in accordance with the invention with a high feed tank. Fig. 2 shows a boiler feed system in accordance with the invention with a low feed tank.

Referring to Fig. L'the steam condenser I is of the regenerative type with a Well 2 in the base of the condenser. The condenser extraction pump 3 draws water from the well 2 and discharges it through a pipe 4 which is in free connection with an elevated surge tank 5 by Way of a V a correspondingly partially open position.

The discharge from the condenser extraction pump 3 can pass direct to the boiler feed pump 1 i by way of a non-return valve i2 and pipes l3 and I 4. The condenser extraction pump 3 is so designed that its maximum capacity is equal to or V sli htly in excess of the maximum capacity of the boiler feed pump H. The elevated feed tank 5 is normally installed at a considerable height above the condenser extraction pump 3 and the boiler feed pump l I so that there is an appreciable pressure above atmosphere in the pipes t, 5, l and the pipes 13 and it between the condenser extraction pump 3 and the boiler feed pump IE, and this pressure prevents the ingress of air and corrosive gases into the water which is being delivered by the condenser extraction pump 3 to the boiler feed pump I I. The condenser extraction pump 3 is so designed that it is capable of handling its maximum capacity with a water level in the condenser well 2 below the low predetermined water level at which the float-controlled valve 3 is full open. In the event ofa failure er the condenser extraction pump 3 the boiler feed pump i i can draw Water direct from the feed tank 5 by way of the pipe 6, non-return valve 12 and pipes l3 and 14. The boiler feed pump 1 I operates at its maximum capacity only in case of emergency and its actual delivery varies in quantity so that there is a continuous flow of water from the condenser extraction pump 3 by way of the pipe 6, pipe i, float-controlled valve 55 and pipe 9 to the condenser l. There is, therefore, a varying quantity of water being continuously circulated and therefore repeatedly subjected to the deaerating action of the regenerative steam condenser i. It will be observed that in normal operationthere is no fiow otwaterffrom theeondenserextractinnapomp "to the t-eed tairleand thatthere'istnoifioun of'water fr'o'm-ithe feed tank d direct into "lthe fee'disystem. 'Any' water which :i-may he taken :from ';the feed tank fismust pass by Way (if itherpipe it lands floatcon'trolled valve 8 intof'the condenser 5| whereinzit is subiected to the deaeratingraction of the "condenser. The lfioat 'controlled valve :8 Jis :made pass a uantity of swater equal .to v-thezmaximum ca'pacity "of the condenser :extra'ction ipuinp when the float it! is at thelow :level. V

- It will be seen that, "in normal 'nperation, the discharge .pressure of the i'condenser text-motion p'umpit is determined:sylthe headfimpcsed'bydzhe feed Ltankxand-thatthere is no possibility 1 water which may be contaminated direct into the "feed system fine-normal operation, hut in thei event "of arstoppage of the mondenser extrasition'pump 3 the boiler steed pump ti will cd Water direct 'fromthe *fee .iztan k-fi. zTv/zo or more steam 'co'nd'ensingr'plants together with two or more feedwtanksifii mayi'b'etasselciatedz togetherand operated in parallel with zcornmon pressure at 'th'e 'point I 5 where'thesseveral condenser extraction pumps and'fee'dtanksare connected to'the suction of the boiler feed pumps. :iniEi'g. 1 there are shown ate-n the discharge wfroiniam 'other condensate extraction pump andat li'A the discharge from :another deaerator extraction pump. This allows the sseveral turbines driven 1 respectively by steam fromzseveralboilers 'to'be operated 'at diiieren't loadings and ensures that the various sets can operatein parallel with the quantitiesof condensate formed in the condensers 'beingsdischarged into the feed systematacommon marrying point and pressure, with no unnecessary transfer of water from feed -.tank to feed tanlgortfrom condenser to condenser.

To ;ensure that wall possible traces of corrosive gases-are removedfrom the condensate-andilfeed v/ater, -there arranged in the .feed :system deaerator .l 6 and .all feed water :required by the boiler'fee'd'pum'p in normaloperationis taken-by Way'of-a pipeflifromtthepipe'i between the connecting points of pipes i5 and '1. .The pipe H pas'sesby'way 'ofithelinlet-valve 1'8 controlled by th'e float IE9 into theideaerato'r ifiz'and inse -doing passes'through aheat exchangerlzfltin Whiclrthe operating steam of an air ejector-ZI is condenser and led back into the ideae'ratorthrough adrain trap 22. Thevairejector 2.! is supplied with opcrating steam through a, pipe @controlled -by valve 23, and Withdraws iair sand'xother inch-eondensable gases from the deaerator It, such air and non-condensable gases being discharged to theatmosphere from the heatexehanger 26] by way of thelair ventapipetZ. The float leis-actuated from a Water level in .a :tank': 25 at -'.the Tease of -the deaieratorfie so that'on'rise of water level in the tankze the fiowiof Water into .thedeaerator is reduced and vice versa. :I-Ieatingsteam from any suitable source is 'ledwjinto -.the tdeaerator by way of-a pipe ze and control valveL-Z'l whichmay be controlled to maintain asubst-antially constant pressure in the deaeratorifi. The dea-erator i5 is provided with a deaerator :extractionipump528 which delivers deaerated ieed Water from the tank 25 into the pipe M which leads the :Water to the suction of the boiler feed p-ump -l I whence the water is discharged by way of a. pipe returns boilers. The pipe 44 isrconnectedibyyzay of the pipe i'3, non-return valve 12 and pipe 'G'toithe feed tank 5,:and the'discharge pressure fromtthe deaerator extraction pump 28 .Jmaintalns :a "substantially constant. discharge'pressureiin -theipipe l deaerating action.

3 fat 3a, predetermined ipressure iin excess not the knead {of feed ital-1k 5 e'so that the 111011 sreturn waive seas kept closed at :allitimes :insnormal: operationiand prevents anyepos$ibi1ity :o'f ideaerate'd watersifrom l'the Jdeaerator 16 being discharged hack to the feed ;tank 5, abut .on failure .of the deaera'toriifiibriof the deaerator extraction pump .;2% 'feed water1 can-:fiow dire'ettfrom the feedtank "5 .by way of the inch-return valve ii 2 iand pipes :lfe (and zt l ti-to the isuctions-ofzthe *kioilerrfeed'pnmp 2H thereby ensuring :the continuity of :the ifee'dzsupply tito Tthe b'oilers.

Anon-return valve 30 is provided on-the .dis- :oharge :of ithe 'sdeaetator :extra'ction pump 28 to preventzfeed wate'r :from Lthe Lf'eedtank 51 entering the deaerater 4| 6 by :wayiof the pump 25 'in the event :of :a ifailure of :said pump. ;The discharge :o'f the #deaerator extraction :pump is .iconneoted to the p rof the -dea'erat'or 'iby way of pipes 3 l, and "the quantity o'f water flowing through the pipes z m'ay E be controlled Ploya valve" 3 2 controlled by the fioat v3t" so arranged that on a fall:of "waterilevel inithe mums 'the-va1vei32 is closed, and asthe-:watenlavel.risesfthevalve: 32 is opened. .The'valves 18 :and'3-2 :maybe combinediin one :valve :a'nd operated ibyva common iflo'at.

The 'capacityfo'f the d'eaerator extraction pump may be equ'al'ito or greater *than the boiler feed pump capacity, and, "since the boiler "feed pump never discharges at lmaX-imum capaoity, in normal operation there is always 'a flow of "Water from the -deaerator extraction ipump 2-8 by way of "the pipe 31 lihto -the ideaerator It and -Water i'iowin'g in this manner is subjected "to'a repeated This arrangement "has the advantage that the:deaeratorsextraction pump is constrained to :operate at substantially constant pressure at all loads of "the boiler feed pump, thereby reducing the rise in discharge "pressure at th'e boiler fe'e'd :pump discharge between run l'oad'and no load 'to that determined by the"chaiacte'ristic of the'b'oilerfeedpuinponly. The-"arrangement is 'suchthat tWO-OIIIIOIG boiler f'ee'd pumps 1! "can'ope'ratestably and satisfactorily in -parallel atali loads, sharing'the total load' in pfoportionwith their head capacity characteristics. All feed Water which is discharged to th'e tdners is-subiect'ed to the double deaeration of the condenser -followedloy' the de'aerator a'nd'in each of these units some'of this feed'wat'er is subjected "to '-'repeated "d'eaeration, thereby enstring the removal of all corrosive gasesat' 'all loads. 'Further, both "the condenser extraction pump 3 and "the deaerator extraction pump "2% are constrained *to operate :at substantially :dohstant dis'ehar'g'e pressures and' with suctionheads which af'e'dn eXces'softheir cavitating Tree sue 'tion h'e'ads, thereby ensuring stability 1 in operation and "freedom from pulping and ensuring that two or more fe'ed systemswill operatest'ably satisfactorily at all loads with a minimum :rise-in feed pump discharge pressure "from full load to no lo'ad. The discharge pressure ofthedea'erato'r extraction pump is determined at the pressure above *the b'oilin'g "point of the 'deaerato'r water necessaryto 'ehsu're hersati'sfactory operation 'of the boiler "feed ump Without cavitation or :instability.

Referring to Fig. -2, the same :numerals :are used 'to-denote similar parts.

The condenser extraction =pump13 -draws water from the leondenser iwell :2 "and discharges .it througha pipe 4 \When'cefit can :pass'by :way of the pipe :l-21 to :the :deaer'ator16,-or,fa1ternatively, by way :oframipeaiflr andpressure-iloaded valve-s35 sharing the total load to the pipe I, from which the water can flow through the float-controlled inlet valve 8 and pipe 9 to the condenser In the event of a failure of the condenser extraction pump 3, the boiler feed pump H can draw water direct from the feed tank by way of the non-return valve l2 and pipes l3 and Hi. The deaerator extracion pump 28 withdraws deaerated water from the deaerator tank and discharges through the non-return valve 39 and the pipe! to the suction of the boiler feed pump ll, which delivers the Water through the pipe 29 to the boilers. The deaerator extraction pump maintains a substantially constant discharge pressure in the pipe i l at a predetermined pressure in excess of the pressure in the deaerator l5 and in excess of the pressure from the water in the feed tank 5, so that the non-return valve I2 is kept closed at all times in normal operation and a pressure aboveatniosphere maintained in the pipelines it and :3, whereby any possibility of ingress of air or conta :iinated water to the feed system is prevented and the discharge of deaerated Water from the deaerator I5 back to the feed tank 5 is prevented by the non-return valve E2. On failure of the deaerator it or the deaerator extraction pump 28, feed water can be drawn direct from the feed tank 5 by way of the non-return valve E2 and pipes i3 and I4 to the suction of the boiler feed pump H, thereby ensuring the continuity or" the feed supply to the boilers. A nonreturn valve 3% is provided on the discharge of the deaerator extraction pump 253 to prevent any feed water from the feed tank 5 entering the deaerator It by way of the deaerator extraction pump 28 in the event of a failure of that pump. I also connect the discharge of the deaerator extraction pump to the top of the deaerator by way 01" pipe 3! and the pressure-loaded valve 35. The capacity of the deaerator extraction pump is equal to or greater than the boiler feed pump capacity so that in normal operation there is always a flow of water from the deaerator extrac tion 25! by way of the pipe 3! and pressureloaded valve into the deaerator IS. The water flowing in this manner is subjected to a repeated deaerating action.

Constant recirculation may be provided between the condenser extraction pump 3 and the condenser E by way of the pipe 3'5 restriction orifice 38, so that there is in continuous circu ation a predetermined quantity of water which is being subjected to a repeated deaerating action. This ensures that the water in the base of the condenser well 2 is always thoroughly deaerated. 'In the same way, I provide a pipe with restriction orifice cc to maintain a constant circulation of water through the deaerator so that the quantity of water in the deaerator tank 25 is always completely deaerated. The arrangement is such that. two or more turbines with their respective condensing plants can be operated charges of the respective condenser extraction pumps 3 married at a common discharge point such as E5. The arrangement further permits two or more boiler feed pumps ii to be operated stably and satisfactorily in parallel at all loads, in proportion with their head capacity characteristics. All feed water which is discharged to the boilers is subjected to the double deaeration or" the condenser followed by the deaerator, and in each of these units some of this feed water is subjected to repeated deaeration, thereby ensuring the removal of all satisfactorily in parallel with the dis corrosive gases at all loads. Further, both the condenser extraction pump 3 and the deaerator extraction pump 28 are constrained to operate at substantially constant discharge pressures and with suction heads which are in excess of their cavitating free suction heads, thereby ensuring stability in operation, freedom from gulping, and ensuring that two or more feed systems will operate stably and satisfactorily at all loads with a minimum rise in feed pump discharge pressure from full load to no load.

The pressure-loaded valves 35 and 36 may be arranged to be automatically controlled by relay apparatus so as to maintain substantially constant discharge pressures at the discharges of the respective pumps 3 and 23.

It will be understood that the invention can be applied to three, four or more condensing plants operating in parallel and also that, while there have been illustrated and described particular arrangements in accordance with the invention, there may be employed other means other than those described to maintain substantially constant pressures at the discharges of the condenser and deaerator extraction pumps in accordance with the invention.

Referring to Fig. 2 it will be understood. that the pressure applied to the surface of the water in the feed tank may be atmospheric pressure or superatmospheric pressure, e. g., of steam or gas.

What is claimed is:

1. A closed feed system for a boiler installation including a condenser for condensing the steam generated in the boiler, a deaerator for deaerating the feed water for the boiler, means including a conduit and a condenser pump therein for conducting condensate from the condenser into the deaerator, a boiler feed water pump, means including a conduit and a deaerator extraction pump therein for conducting deaerated feed water from the deaerator to the inlet of the boiler feed pump, an external feed water tank arranged to supply feed water at a superatmospheric pressure, piping connecting the external feed tank with the conduit connected to the inlet of the boiler feed water pump for supplying Wa ter to the boiler feed water pump if the deaerator extraction pump should fail, a non-return valve in said piping, said deaerator extraction pump having a discharge pressure substantially in excess of the pressure on the water in the piping from the feed Water tank, whereby feed water is normally supplied to the boiler feed pump only by the deaerator extraction pump,

v a valve-controlled conduit for conducting water from the feed tank into the condenser, pipe means for conducting condensate from the condenser pump into said valve-controlled conduit up-stream of the valve therein, and control means operatively associated with the condenser extraction pump and the deaerator extraction pump adapted to maintain a substantially constant flow of water through said extraction pumps at substantially predetermined constant discharge pressures at the discharge outlets of said extraction pumps.

2. A closed feed system as claimed in l, in which said pipe means is provided with a valve responsive to the discharge pressure or the condenser pump. 7

3. A closed feed system as claimed in claim 1, including an orifice-controlled pipe connected into the conduit leading from the condenser pump and into the condenser for providing a constant flow of condensate from the outlet of the condenser pump into the condenser for deaeration therein.

4. A closed feed system for a boiler installation including a condenser for condensing the steam generated in the boiler, a deaerator for deaerating the feed water for the boiler, means including a conduit and a condenser extraction pump therein for conducting condensate from the condenser into the deaerator, a boiler feed water pump, means including a conduit and a deaerator extraction pump therein for conducting deaerated feed water from the deaerator to the inlet of the boiler feed pump, an external feed water tank arranged to supply feed water at a superatmospheric pressure, piping connecting the external feed tank with the conduit connected to the inlet of the boiler feed water pump for supplying water to the boiler feed water pump if the deaerator extraction pump should fail, a non-return valve in said piping, said deaerator extraction pump having a discharge pressure substantially in excess of the pressure on the water in the piping from the feed water tank, whereby feed water is normally supplied to the boiler feed pump only by the deaerator extraction pump, and control means operatively associated with the condenser extraction pump and the deaerator extraction pump adapted to maintain a substantially constant flow of water through said extraction pumps at substantially predetermined constant discharge pressures at the discharge outlets of said extraction pumps.

5. A closed feed system for a boiler installation including a condenser for condensing the steam generated in the boiler, a deaerator for deaerating the feed water for the boiler, means including a conduit and a condenser extraction pump therein for conducting condensate from the condenser into the deaerator, a boiler feed water pump. means including a conduit and a deaerator extraction pump therein for conducting deaerated feed water from the deaerator to the inlet of the boiler feed pump, an external feed water tank arranged to supply feed water at a superatmospheric pressure, piping connecting the external feed tank with the conduit connected to the inlet of the boiler feed water pump for supplying water to the boiler feed water pump if the deaerator ex-- traction pump should fail, a nonreturn valve in said piping, said deaerator extraction pump having a discharge pressure substantially in excess of the pressure on the Water in the piping from the feed water tank, whereby feed water is normally supplied to the boiler feed pump only by the deaerator extraction pump, an orifice-controlled pipe connecting the discharge outlet of the condenser pump with the condenser, and an orifice-controlled pipe connecting the discharge outlet of the deaerator extraction pump with the upper part of the deaerator to maintain a substantially constant flow of Water through said extraction pumps at substantially predetermined constant discharge pressures at the discharge outlets of said extraction pumps.

6. In the processing of feed water to be supplied to a boiler comprising a part of the closed feed system including a condenser for the boiler, the steps comprising providing a source of boiler feed water arranged to supply feed water at a superatmospheric pressure, maintaining a body of condensate in the condenser, pumping a stream of condensate from the condenser into a deaerating zone in which the condensate is subjected to deaerating conditions and the resulting deaerated condensate accumulated in a body, pumping a stream of deaerated condensate from said body of deaerated condensate and passing at least a portion thereof to the inlet of a boiler feed water pump, passing a stream of water from said water source into the stream of deaerated condensate flowing to the boiler feed water pump when said stream of deaerated condensate is insufficient to supply the requirements of the boiler feed water pump, and under normal operating conditions maintaining the pressure on the stream of deaerated condensate flowing to the boiler feed pump in excess of the pressure on the water from the feed water source, whereby the flow of water from the feed water source directly to the boiler feed pump is prevented.

7. The processing of feed water as claimed in claim 6 in which said source of feed water includes a hydrostatic head of water in a column providing water under superatmospheric pressure at the level of the condenser, and including the steps of passing the stream of condensate from said condenser into said column, passing condensate from said column into the deaerating zone, and passing a controlled flow of condensate from said column of water into the condenser.

8. The processing of feed water as claimed in claim 6, in which the streams of condensate and deaerat'ed condensate are maintained at substantially predetermined constant pressures and delivered by the respective pumping operations at substantially constant rates of flow.

9. A closed feed system for a boiler installation including a condenser for condensing the steam generated in the boiler, a deaerator for deaerating the feed water for the boiler, means including a conduit and a condenser extraction pump therein for conducting condensate from the condenser into the deaerator, a boiler feed water pump, means including a conduit and a deaerator ex traction pump therein for conducting deaerated feed Water from the deaerator to the inlet of the boiler feed pump, an external feed water tank located at a higher level than said condenser and arranged to supply feed water at a superatmospheric pressure, piping connecting the external feed tank with the conduit connected to the inlet of the boiler feed water pump for supplying water to the boiler feed water pump if the deaerator extraction pump should fail, a non-return valve in said piping, said deaerator extraction pump having a discharge pressure substantially in excess of the pressure on the water in the piping from the feed water tank, whereby feed water is normally supplied to the boiler feed pump only by the deaerator extraction pump, a pipe connected into said piping lip-stream of said nonreturn valve and connected into said condenser, a valve in said pipe, a float in said condenser controlling the valve in said pipe, and a water flow connection between the condenser pump conduit and a point of said piping upstream of the nonreturn valve therein.

HAROLD HILLIER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,636,361 Gibson July 19, 1927 1,991,929 Hillier Feb. 19, 1935 2,371,443 Hillier Mar. 13, 1945 FOREIGN PATENTS Number Country Date 141,015 Great Britain .Nov. 18, 1920 207,136 Great Britain Nov. 22, 1923 211,924 Great Britain Feb. 22, 1924 

